The appeal of the use of one or more swash plates has produced many designs and the building of many models. For example, see the chapter entitled "Engines with Unusual Translation of Power" in the book by LJK Setright entitled "Some Unusual Engines" published by Mechanical Engineering Publications Limited, London." In that chapter it is stated: "It is an arrangement that has charmed designers for many years because it is blessedly compact, with the cylinders of the engine arranged in the same way as are the chambers of a revolver. With an output shaft at the center of the cylinder block, all that is needed to link it to the pistons is a swash palte or wobble plate. Could anything be simpler or more obvious?"
The apparent simplicity of the swash plate and the compactness of a possible engine or a pump is the main attraction. This is particularly true of multiple cylinder machines.
A basic machine can be seen in U.S. Pat. No. 3,006,324 where the centrally located swash plate is driven by half-spheres which, in turn, are driven by opposed pistons. Consider what happens when the shaft rotates, for example, at 4000 RPM. One side of each driving element must rub against the swash plate, and the other, spherical side of each element must rotate in its concave spherical seat. Such design, obviously leads to low efficiency and short life.
A major effort to overcome the high speed friction of a simple swash plate is exemplified by U.S. Pat. No. 2,877,653 where the swash plate is replaced by a Z shaped drive shaft that is coupled by a set of ball bearings to a driving plate. This plate no longer revolves but is wobbled by ball and socket devices that are driven by the pistons. Again, as in the previously mentioned example, the ball and socket devices must not only slide on the shafts of the driving plate, but must slide radially against the extensions of the cylinders.
Another attempt to reduce the frictions inherent in many swash plate designs can be seen in Reagan, U.S. Pat. No. 1,978,762. Here the usual swash plate is divided into two opposing swash plates between which is located a single flat drive plate, coupled to the two swash plates by a ball bearing assembly. While this reduces the friction between these elements, the outer rim of the drive plate is coupled by friction means to sliding pistons. This friction means consist of hemispheres that contact the drive plate on their flat inner surfaces. The frictional contact between those hemispheres and the sliding pistons as well as the frictional contact between the drive plate and the inner walls of the hemispheres produce the wear that has plaqued swash plate machines for decades.
In order to overcome the sliding frictions of the driving joints of the machine such as is mentioned in U.S. Pat. No. 2,877,653 connecting rods were introduced between the pistons and the non rotating drivers of the Z shafts as exemplified in U.S Pat. Nos. 3,528,394 and 4,497,284. This solution eliminates some sliding joints but requires that the connecting rods have ball-and-socket joints at both ends, or a ball and socket at one end and a universal joint at the other end of each connecting rod. This type of construction gives rise to another difficulty. There is now no mechanism to keep the driving plate from rotating because the connecting rods do not constrain the plate from rotation. In U.S. Pat. No. 3,528,394 the two driving plates have extension pins (28 in FIG. 1) that ride in guides (29) formed in the frame of the machine so as to keep the plates from turning. Such construction leads to noise and rapid wear. Such a sliding anti-rotation device can be seen at 13 in FIG. 1 of U.S. Pat. No. 1,370,927.
Now, I come to another problem that has plagued designers of swash plate machines that do not use double hinged connecting rods. If a driving plate is driven by a ball joint such as shown in U.S. Pat. No. 1,610,060 or in U.S. Pat. No. 4,285,303, one of the ball joints can have a linear motion when driven by one or two opposed pistons. By "linear," I mean in a plane passing through the center line of the main shaft. The ball joint on the opposite side of the machine, that is where there are two (or two sets of opposed pistons), also move in a linear motion in a plane parallel to the main shaft. However, the ball joints 90% to these two no longer can move in such a linear modes without sliding in some way on the driving plate. For this reason in U.S. Pat. No. 4,285,303 the inventor shows sliding freedom between plate 23 and ball joint 51 in FIG. 7, and the same arrangement in FIG. 8. In FIG. 3 of U.S. Pat. No. 1,610,060 we see a similar solution provided by looseness between the ball joint assemblies 10 and circular spaces 9 in FIG. 3.
The expedients just mentioned provide undetermined motion and provide violent impacts, noise and rapid wear at these areas.
An interesting method of holding the driving plate from turning but permitting it to wobble is shown in U.S. Pat. No. 4,497,284. Here the plate is mounted on a bearing in a gimbal ring and the gimbal ring is mounted on a bearing in the machine case. The machine connecting rods as is done in others.
Two sets of opposed pistons, spaced 180.degree. apart in a swash plate machine do not have the problem described above but the chance to employ more cylinders, particularly eight, is highly desirable.
It should be noted that in all of the patents that I have studied, friction between sliding components exists in several places, and it is not surprising that so far no swash plate internal combustion engine has been commercially successful.